Nosocomial infections are a major cause of morbidity and mortality in burn patients. We propose to study the pathogenesis of organisms causing infections in burn patients (e.g. Pseudomonas aeruginosa, Candida albicans), and to assess the effect of prophylactic and therapeutic regimen on the course of infection. We also will study the interaction of one virulence associated factor, pseudomonas exotoxin A (PE) with cultured mammalian cells; here the goal is to determine the cellular basis for toxin susceptibility. A burn mouse model requiring low numbers of organisms for lethality will be used to measure the protection afforded by human immunoglobulin modified for intravenous use (IGIV). Antibodies in both pooled normal and hyperimmune preparations will be characterized. Proteolytic enzymes contribute to virulence of P. aeruginosa; therefore studies on protection with protease inhibitors (e.g. Alpha2 macroglobulin) will be continued. These inhibitors will be given alone, or in conjuction with IGIV therapy. Finally the virulence of other opportunistic pathogens, including Klebsiella pneumoniae and C. albicans will be evaluated in the burn mouse model. Cross protection studies with pooled normal human IGIV will be included. Production of PE is required for expression of maximal virulence by P. aeruginosa. The intracellular route of movement of toxin will be compared in toxin sensitive and resistant cells, and the site (organelle) at which it is activated will be determined. Biochemical and electron microscopic studies are run in parallel. Direct visualization of toxin (biotinyl toxin:avidin gold system) will be compared with localization of iodinated toxin by subcellular frationation. The isolation and initial characterization of toxin binding proteins on the mouse fibroblast surface will be attempted.